Conventional motors in compressors used in heat pump devices and the like have high torque when compressing a refrigerant and have low torque when discharging a compressed high-pressure refrigerant; therefore, torque variation (load change) occurs. Due to the occurrence of such torque variation, deflection of the shaft occurs and thus vibration and noise are generated when the compressor is operating.
In order to suppress such vibration and noise, balance weights have been arranged on the end portions of the rotor of the motor. With the balance weights, the force acting on the entire rotating portion is balanced so that the deflection of the shaft due to the compression of the refrigerant is eliminated, thereby suppressing vibration and noise generated when the compressor is operating.
In contrast, a motor with no such balance weights has been developed. For example, a technology is disclosed in Patent Literature 1 in which the motor has a configuration in which, in order to eliminate balance weights that suppress the load change of the motor, one of the opposed permanent magnets generates a magnetomotive force larger than that of the other of the opposed permanent magnets and the air gap between the stator and one of the opposed permanent magnets is made larger than the air gap between the stator and the other of the opposed permanent magnets.